The giraffe’s long neck : From evolutionary fable to whole organism
A LONE GIRAFFE BULL STOOD at the edge of the scrubby bush forest that opened into a grassland. It was August, the beginning of spring, but also the middle of the dry season in the southern African savannah. The grasses and forbs were yellowed and brittle. Many trees and bushes had no leaves, though some still […]
Blood pressure and flow rate in the giraffe jugular vein
Experimental measurements in the jugular veins of upright giraffes have shown that the internal pressure is somewhat above atmospheric and increases with height above the heart. A simple model of steady viscous flow in an inverted U-tube shows that these observations are inconsistent with a model in which the blood vessels in the head and […]
Does gravitational pressure of blood hinder flow to the brain of the giraffe?
Vascular pressure consists of the sum of two pressures: (a) pressure developed by the pumping of the ventricles against the resistance of vessels, designated as viscous flow pressure, and (b) pressure caused by gravity, traditionally called hydrostatic, better described as gravitational pressure. In a conduit, both of these pressures must be overcome when a liquid […]
Haemodynamics of the jugular vein in the giraffe
Controversy cotinues over the haemodynamics of the circulation to and from the head of the giraffe. The recent study by Hargens et al. provides new information explaining the absence of oedema in the legs of the ambulant giraffe. But in sedated, standing giraffes the pressure gradient down the jugular vein is about one-tenth of, and […]
Origin of mean arterial and jugular venous blood pressures in giraffes
Using a mechanical model of the giraffe neck and head circulation consisting of rigid, ascending, ‘carotid’ limb, a ‘cranial’ circulation that could be rigid or collapsible, and a descending, ‘jugular’ limb that also could be rigid or collapsible, we have analyzed the origin of the high arterial and venous pressures in giraffe, and whether blood […]